Performance regulation of a thin film composite (TFC) NF membrane by low-temperature interfacial polymerization assisted by the volatilization of n-hexane

Abstract

Reducing the thickness of the polyamide (PA) layer has been confirmed as a feasible strategy to improve the permeability of the thin film composite (TFC) nanofiltration (NF) membrane. In this study, a novel interfacial polymerization (IP) approach assisted by the volatilization of n-hexane was proposed to promote the formation of a thinner PA layer, in which a small amount of n-hexane was added onto the substrate membrane after aqueous phase immersion and before the organic phase coating, then the temperature of the substrate membrane together with the water-soluble monomer solution would be decreased due to the volatilization of n-hexane. The infrared thermographies demonstrated that 7.8 μL cm−2n-hexane dosage was the most efficient, which can sharply decrease the surface temperature from room temperature (25 °C) to 7.9 °C. The TFC membranes prepared at the lower temperature presented much higher permeability. When PIP concentration was 0.3% w/v, TMC concentration was 0.1% w/v and IP reaction time was 40 s, the PA layer formed at this low temperature was smoother and more hydrophilic. Its thickness was reduced from 26.97 nm to 11.98 nm and water permeability was increased by 50% to 36.7 L m−2 h−1 bar−1 while maintaining Na2SO4 rejection of 96.5%.